Change userId to required in operations that would otherwise throw exceptions

Jellyfin.Api/Controllers/ItemsController.cs

@@ -143,7 +143,7 @@ namespace Jellyfin.Api.Controllers
         [HttpGet("Items")]
         [ProducesResponseType(StatusCodes.Status200OK)]
         public ActionResult<QueryResult<BaseItemDto>> GetItems(
-            [FromQuery] Guid? userId,
+            [FromQuery] Guid userId,
             [FromQuery] string? maxOfficialRating,
             [FromQuery] bool? hasThemeSong,
             [FromQuery] bool? hasThemeVideo,
@@ -224,8 +224,8 @@ namespace Jellyfin.Api.Controllers
             [FromQuery] bool enableTotalRecordCount = true,
             [FromQuery] bool? enableImages = true)
         {
-            var user = userId.HasValue && !userId.Equals(Guid.Empty)
-                ? _userManager.GetUserById(userId.Value)
+            var user = !userId.Equals(Guid.Empty)
+                ? _userManager.GetUserById(userId)
                 : null;
             var dtoOptions = new DtoOptions { Fields = fields }
                 .AddClientFields(Request)

Jellyfin.Api/Controllers/TrailersController.cs

@@ -114,7 +114,7 @@ namespace Jellyfin.Api.Controllers
         [HttpGet]
         [ProducesResponseType(StatusCodes.Status200OK)]
         public ActionResult<QueryResult<BaseItemDto>> GetTrailers(
-            [FromQuery] Guid? userId,
+            [FromQuery] Guid userId,
             [FromQuery] string? maxOfficialRating,
             [FromQuery] bool? hasThemeSong,
             [FromQuery] bool? hasThemeVideo,